With the ever increasing use of electrical power in the home, there is a growing governmental and public awareness of electrical shock hazard and recognition of the need for improved means to reduce or eliminate the possibility of harmful electrical shock. This has resulted in a mandating of more sophisticated protection, requiring use of means considered most effective, but within the restricting framework of cost that affects the matter of practical implementation.
If one can never presume to place a price on human life, the cost of protecting it should not be a factor, but it is one that is constantly at work in the marketplace. Maximum electrical shock protection should ideally be provided in all instances, but there is a demonstrated willingness to accept risk in the interest of economy and especially to forego safety modifications that might escalate the price of less expensive items. The cost of adding ground fault and line-to-line protection to hairdryers is more acceptable than when added to hair curlers, where the cost of the protection may well exceed the basic cost of the appliance yet the curler can be as dangerous as the dryer.
These examples were selected because conditions of greatest electrical shock hazard have been generally established to exist wherever appliances are used around water, but most particularly in the bathroom where intensive use of electrical appliances is combined with extreme proximity to water under widely variable conditions, many of which include a ready opportunity for complete or partial immersion, It thus appeared that a simple yet effective device which needed only to interrupt power to the appliance in the event of its immersion could provide shock protection in a majority of hazardous instances and might be produced at lower cost than, for example, those described in my U.S. Pats. No. 3,997,818 and 4,707,759, which are designed to protect under a very broad spectrum of hazardous conditions.
While many immersion detection circuit interrupter devices have been designed and marketed, it is believed that the present invention more closely approaches the goal of providing maximum effectiveness with minimum cost in order to achieve the most extensive use. The expense of electromagnetic switching devices is avoided, and where solid state devices are employed, their closed mode of failure is made to represent a positive fail-safe factor rather than a negative consideration in the matter of protective functioning. The present invention is particularly rapid in its protection due to a shorting technique which diverts current from the appliance circuit through a low resistance path as it activates the permanent interruption device. It uses very few electronic components and has a simplified construction which is due in part to its single service design. While accidental immersion of an electrical appliance is included in the most hazardous of shock scenarios, such scenarios may be expected to be extremely rare in the course of normal human experience and the expense of making a protective device resettable would appear to be not only superfluous but counterproductive in the attempt to minimize cost, unless a device is prone to the annoyance of unwarranted interruption and thus has a particular need to be made resettable. Safeguards against unwarranted interruption are provided in the present invention and the fast acting fuse link in the interrupter mechanism typically has a current rating far below that of the standard overcurrent devices installed for the protection of branch circuits so that the shorting technique does not result in an interruption of the branch service. However, the rarity of an immersion mishap should prevent such a branch interruption from being considered an aggravation and fuse links designed to permit use with appliances having greater current demands may become permissible.